Reversible encephalopathy after cardiac transplantation: histologic evidence of endothelial activation, T-cell specific trafficking, and vascular endothelial growth factor expression.

Reversible encephalopathy after transplantation is well recognized. The condition is commonly thought to be related to immune suppression, and a characteristic brain imaging pattern is typically recognized with vasogenic edema in the parietal and occipital regions, typically termed posterior reversible encephalopathy syndrome (PRES). We report the case of a patient with reversible encephalopathy after cardiac transplantation with brain biopsy evidence of endothelial activation, selective intravascular/perivascular T-cell trafficking, and VEGF expression in astrocytes, neurons, and the endothelium.

Diffuse alterations in synaptic protein expression following focal traumatic brain injury in the immature rat.

INTRODUCTION: The mechanisms responsible for cognitive decline after traumatic brain injury (TBI) in pediatric patients are poorly understood. The present study examined the potential role of synaptic alterations in this process by using an animal model of immature head injury to define the impact of TBI on expression of the synaptic protein, synaptophysin. MATERIALS AND METHODS: After craniotomy, TBI was induced in postnatal day 17 (PND17) rats using controlled cortical impact delivered to the left hemisphere. NeuN, a neuronal marker, and synaptophysin expression were examined 1 day, 1 week, and 1 month after injury by immunohistochemistry and immunoblotting. RESULTS: There were significant decreases in both NeuN and synaptophysin after 1 day and 1 week but not 1 month after injury within the hippocampus and neocortex adjacent to the impact site compared to sham-injured controls. The decrease in synaptophysin and NeuN was also noted in the contralateral hippocampus by 1 day after injury and in the contralateral neocortex by 1 week, indicating that changes in protein expression were not solely localized to the injury site but occurred in more distant regions as well. DISCUSSION: In conclusion, the decrease and recovery in synaptophysin parallel the cognitive changes that occur after experimental TBI in the PND17 rat, which suggests that changes in this protein may contribute to cognitive declines after injury. The results also suggest that, in spite of the focal nature of the impact, diffuse alterations in protein expression can occur after immature TBI and may contribute to the subsequent cognitive dysfunction.

Cell surface tumor endothelial markers are conserved in mice and humans.

We recently identified genes encoding tumor endothelial markers (TEMs) that displayed elevated expression during tumor angiogenesis. From both biological and clinical points of view, TEMs associated with the cell surface membrane are of particular interest. Accordingly, we have further characterized four such genes, TEM1, TEM5, TEM7, and TEM8, all of which contain putative transmembrane domains. TEM5 appears to be a seven-pass transmembrane receptor, whereas TEM1, TEM7, and TEM8 span the membrane once. We identified mouse counterparts of each of these genes, designated mTEM1, mTEM5, mTEM7, and mTEM8. Examination of these mTEMs in mouse tumors, embryos, and adult tissues demonstrated that three of them (mTEM1, mTEM5, and mTEM8) were abundantly expressed in tumor vessels as well as in the vasculature of the developing embryo. Importantly, expression of these mTEMs in normal adult mouse tissues was either undetectable or detected only in a small fraction of the vessels. These results demonstrate conservation of human and mouse tumor angiogenesis at the molecular level and support the idea that tumor angiogenesis largely reflects normal physiological neovasculaturization. The coordinate expression of TEM1, TEM5, and TEM8 on tumor endothelium in humans and mice makes these genes attractive targets for the development of antiangiogenic therapies.

Characterization of MAD2B and other mitotic spindle checkpoint genes.

Aneuploidy is a characteristic of the majority of human cancers, and recent work has suggested that mitotic checkpoint defects play a role in its development. To further explore this issue, we isolated a novel human gene, MAD2B (MAD2L2), which is homologous to the spindle checkpoint gene MAD2 (MAD2L1). We determined the chromosomal localization of it and other spindle checkpoint genes, including MAD1L1, MAD2, BUB3, TTK (MPS1L1), and CDC20. In addition, we resolved the genomic intron-exon structure of the human BUB1 gene. We then searched for mutations in these genes in a panel of 19 aneuploid colorectal tumors. No new mutations were identified, suggesting that genes yet to be discovered are responsible for most of the checkpoint defects observed in aneuploid cancers.

Post-transcriptional silencing of RET occurs, but is not required, during raf-1 mediated differentiation of medullary thyroid carcinoma cells.

Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor of the calcitonin secreting thyroid C-cells. Somatic and germline mutations in the RET proto-oncogene are associated with sporadic and inherited cases of MTC, respectively. The human MTC cell line, TT, can be differentiated by activated raf-1. This differentiation is characterized, in part, by down-regulation of the RET proto-oncogene. We now show that raf-1 induction is followed by activation of the downstream kinases MEK1/2 and ERK1/2 and that differentiation is dependent on activation of MEK1/2. The concurrent down-regulation of RET appears to involve altered nuclear compartmentalization and transport of RET mRNA. Although RET is down-regulated during raf-1 mediated differentiation, overexpression of activated RET alleles which resist down-regulation does not alter the raf-1 mediated differentiation response. These data suggest that RET down-regulation is associated with, but not required, for raf-1 mediated MTC cell differentiation and that the raf-1 signal transduction pathway plays a dominant role in promoting MTC cell differentiation.

Differentiation of medullary thyroid cancer by C-Raf-1 silences expression of the neural transcription factor human achaete-scute homolog-1.

BACKGROUND: Human achaete-scute homolog-1 (hASH1), a fetal neural transcription factor, is highly expressed in neuroendocrine tumors such as medullary thyroid cancer (MTC). Although hASH1 probably plays a part in the growth and development of these tumors, its precise role and mechanism are unknown. METHODS: To further elucidate the function and regulation of hASH1 in neuroendocrine tumor differentiation, we used a model of MTC tumor differentiation mediated by the ras/raf-1 signaling pathway. The MTC TT cells alone or transduced with a beta-estradiol activatable raf-1 construct (TT: delta Raf-1:ER) were treated with beta-estradiol or carrier. Northern analysis and nuclear run-off assays were performed to determine the hASH1 messenger RNA (mRNA) levels and transcription rate, respectively. RESULTS: The TT: delta Raf-1:ER cells treated with beta-estradiol underwent marked biochemical and morphologic changes, including cell rounding, increase in calcitonin transcription, loss of RET proto-oncogene expression, and cessation of cell growth. During this differentiation process expression of hASH1 mRNA was silenced. Nuclear run-off experiments revealed that this decrease in steady-state hASH1 mRNA by raf-1 activation resulted predominantly from transcriptional inhibition. CONCLUSIONS: Silencing of hASH1 in parallel with loss of RET is associated with development of a mature C-cell differentiation pattern. Mechanisms leading to transcriptional silencing of hASH1 may be crucial in regulating the proliferative capacity or differentiation status of MTC. Downstream targets of hASH1 could play a role in C-cell proliferation and progression to MTC.